Cyclohexanone is an important product in the chemical industry and is useful as, for example, an industrial solvent, as an activator in oxidation reactions and in the production of adipic acid, cyclohexanone resins, cyclohexanone oxime, caprolactam and nylon 6.
Currently, the most common route for the production of cyclohexanone is by oxidation of cyclohexane to cyclohexyl hydroperoxide, which is then cleaved to produce cyclohexanol and cyclohexanone in substantially equimolar amounts.
Another potential route for the production of cyclohexanone is by a variation of the Hock process, in which benzene is converted to cyclohexylbenzene and the cyclohexylbenzene is oxidized to produce cyclohexylbenzene hydroperoxide, which is then cleaved to produce cyclohexanone and phenol in substantially equimolar amounts. This route has the potential advantage that phenol is a highly valued intermediate in the production of phenolic resins, bisphenol A, ε-caprolactam, adipic acid, and plasticizers.
One problem in producing phenol by way of the cleavage of cyclohexylbenzene hydroperoxide is that the cyclohexanone and phenol form an azeotropic mixture composed of 28 wt % cyclohexanone and 72 wt % phenol. Thus any attempt to separate the cleavage effluent by simple distillation results in this azeotropic mixture. Moreover, any unnreacted cyclohexylbenzene in the cleavage effluent will co-distill with the azeotropic mixture. A further potential problem with the cyclohexylbenzene route to cyclohexanone is that, although both phenol and cyclohexanone are valuable commodities with growing markets, it would be useful to have a technology for balancing the supply and demand between these two products.
The present invention seeks to address these problems by providing a process for producing cyclohexanone by oxidation of cyclohexylbenzene to cyclohexylbenzene hydroperoxide followed by cleavage of the cyclohexylbenzene hydroperoxide, in which at least a portion of the effluent from the cleavage step is subjected to a selective hydrogenation step. The hydrogenation step converts at least part of the phenol in the effluent portion to additional cyclohexanone. Although the cleavage effluent portion subjected to the hydrogenation step can be a substantially pure phenol fraction separated from the raw effluent, given the cost of this separation, the process can also be applied to an effluent portion containing some or all of the cyclohexanone produced in the cleavage step. In this way, the total cost of purifying the final cyclohexanone stream and, if present, the final phenol stream can be minimized. Then, depending on the then current demand for phenol, part or all of the cyclohexanone could be dehydrogenated back to phenol. Alternatively, all the cyclohexanone could be recovered as saleable product.